Technical Abstract:
Genetic relatedness was estimated among 34 plant introduction accessions (PIs) of the genus Citrullus (of these, 30 PIs are known to have disease resistance) and five watermelon cultivars, using 28 RAPD primers. These primers produced 662 RAPD markers that could be scored with high confidence. Based on these markers, genetic similarity coefficients were calculated and a dendrogram was constructed using the unweighted pair-group method with arithmetic average (UPGMA). The analysis delineated three major clusters. The first cluster consisted of a subcluster of five watermelon cultivars, a subcluster of C. lanatus var. lanatus accessions, and a subcluster of C. lanatus var. lanatus accessions that contained some C. lanatus var. citroides genes. The second cluster consisted of the C. lanatus var. citroides accessions while the third cluster consisted of the C. colocynthis accessions. The two C. lanatus clusters differentiated from each other and from the C. colocynthis cluster at the level of 58.8% and 38.9% genetic similarity. The results in this study indicated higher genetic variation within C. colocynthis and C. lanatus var. citroides as compared to C. lanatus var. lanatus (average genetic similarity value within each cluster was 74.2%, 82.8% and 87.5%, respectively). As expected, the lowest genetic variation was among the five watermelon cultivars (93.1% average genetic similarity).